Vehicle systems and loss of isolation detection methods

Abstract

Vehicles and related systems and monitoring methods are provided for detecting a loss of isolation on one side of a power converter. One method involves monitoring a normalized voltage input to a power conversion module coupled to the electric motor, in response to the normalized voltage exceeding a diagnostic activation threshold, determining a first number of instances of a range between successive extremas of the normalized voltage exceeding a loss of isolation range threshold over a diagnostic window of time, and automatically initiating a remedial action when the first number is greater than a loss of isolation detection threshold.

What is claimed is: 
     
       1. A method of monitoring an electric motor in a vehicle, the method comprising:
 monitoring, by a control module, a normalized voltage to a power conversion module coupled to the electric motor; 
 detecting that the normalized voltage exceeds a diagnostic activation threshold; 
 in response to the normalized voltage exceeding the diagnostic activation threshold, determining a first number of instances of a range between successive extremas of the normalized voltage exceeding a loss of isolation range threshold over a diagnostic window of time after detecting the normalized voltage exceeding the diagnostic activation threshold; and 
 automatically initiating a remedial action when the first number of instances of the range is greater than a loss of isolation detection threshold by automatically generating a diagnostic code associated with the electric motor. 
 
     
     
       2. The method of  claim 1 , further comprising detecting an alternating current (AC) loss of isolation event after verifying a respective mean value associated with a respective instance of the successive extremas of the normalized voltage is within a threshold of a normalized voltage value, wherein automatically initiating the remedial action further comprises automatically providing an indication of the AC loss of isolation event. 
     
     
       3. The method of  claim 2 , wherein the automatically providing the indication comprises the control module automatically generating a notification to a user via an output device to inspect the electric motor during a next maintenance event. 
     
     
       4. The method of  claim 1 , further comprising detecting a direct current (DC) loss of isolation event when a difference between a respective mean value associated with a respective instance of the successive extremas of the normalized voltage and a normalized voltage value is greater than a threshold, wherein automatically initiating the remedial action further comprises automatically providing an indication of the DC loss of isolation event. 
     
     
       5. The method of  claim 1 , wherein monitoring the normalized voltage comprises:
 obtaining a measured voltage for a reference node associated with a voltage bus coupled between an energy source and the power conversion module relative to a ground reference node; and 
 dividing the measured voltage by a direct current (DC) voltage associated with the energy source to obtain the normalized voltage. 
 
     
     
       6. The method of  claim 1 , further comprising extracting the instances of the successive extremas of the normalized voltage during the diagnostic window of time, wherein a respective instance of the successive extremas comprises a respective maxima of the normalized voltage and a respective minima of the normalized voltage. 
     
     
       7. The method of  claim 6 , further comprising subtracting the respective minima of the normalized voltage from the respective maxima of the normalized voltage to obtain a respective range value associated with the respective instance of the successive extremas, wherein determining the first number of instances comprises incrementing a counter when the respective range value is greater than the loss of isolation range threshold. 
     
     
       8. The method of  claim 7 , wherein automatically initiating the remedial action comprises automatically initiating the remedial action when a value of the counter is greater than the loss of isolation detection threshold. 
     
     
       9. The method of  claim 1 , wherein monitoring the normalized voltage comprises:
 determining a midpack voltage between a node of a voltage bus coupled between an energy source and the power conversion module and a vehicle chassis ground reference voltage node; 
 dividing the midpack voltage by a direct current (DC) voltage associated with the energy source to obtain a normalized midpack voltage; and 
 monitoring the normalized midpack voltage. 
 
     
     
       10. The method of  claim 9 , wherein determining the first number of instances comprises counting the first number of instances when the range between a respective pair of peak and valley values for the normalized midpack voltage is greater than the loss of isolation range threshold within the diagnostic window of time. 
     
     
       11. The method of  claim 10 , wherein automatically initiating the remedial action comprises automatically providing an indication of an alternating current (AC) loss of isolation event when the first number of instances of the range between respective pairs of peak and valley values for the normalized midpack voltage is greater than the loss of isolation range threshold within the diagnostic window of time is greater than an AC loss of isolation detection threshold number. 
     
     
       12. The non-transitory computer-readable medium of  claim 11 , wherein the monitoring service is configurable to extract the instances of the successive extremas of the normalized voltage during the diagnostic window of time, wherein a respective instance of the successive extremas comprises a respective maxima of the normalized voltage and a respective minima of the normalized voltage. 
     
     
       13. The non-transitory computer-readable medium of  claim 12 , wherein the monitoring service is configurable to subtract the respective minima of the normalized voltage from the respective maxima of the normalized voltage to obtain a respective range value associated with the respective instance of the successive extremas, wherein determining the first number of instances comprises incrementing a counter when the respective range value is greater than the loss of isolation range threshold. 
     
     
       14. A non-transitory computer-readable medium comprising executable instructions that, when executed by a processor, cause the processor to provide a monitoring service configurable to:
 monitor a normalized voltage to a power conversion module coupled to an electric motor of a vehicle; 
 detect that the normalized voltage exceeds a diagnostic activation threshold; 
 in response to the normalized voltage exceeding the diagnostic activation threshold, determine a first number of instances of a range between successive extremas of the normalized voltage exceeding a loss of isolation range threshold over a diagnostic window of time after detecting the normalized voltage exceeding the diagnostic activation threshold; and 
 automatically initiate a remedial action when the first number of instances of the range is greater than a loss of isolation detection threshold by automatically generating a diagnostic code associated with the electric motor. 
 
     
     
       15. The non-transitory computer-readable medium of  claim 14 , wherein the monitoring service is configurable to detect an alternating current (AC) loss of isolation event after verifying a respective mean value associated with a respective instance of the successive extremas of the normalized voltage is within a threshold of a normalized voltage value, wherein automatically initiating the remedial action further comprises automatically providing an indication of the AC loss of isolation event. 
     
     
       16. The non-transitory computer-readable medium of  claim 14 , wherein the monitoring service is configurable to detect a direct current (DC) loss of isolation event when a respective mean value associated with a respective instance of the successive extremas of the normalized voltage is greater than a normalized voltage value by more than a threshold, wherein automatically initiating the remedial action further comprises automatically providing an indication of the DC loss of isolation event. 
     
     
       17. A vehicle system including:
 an electric motor; 
 a direct current (DC) voltage bus comprising a reference voltage node; 
 a power conversion module coupled between the DC voltage bus and the electric motor; and 
 a control module coupled to the power conversion module to provide a monitoring service configurable to:
 monitor a normalized voltage to the power conversion module comprising a relationship between a measured voltage of the reference voltage node and a DC voltage associated with the DC voltage bus; 
 detect that the normalized voltage exceeds a diagnostic activation threshold; 
 in response to the normalized voltage exceeding the diagnostic activation threshold, determine a first number of instances of a range between successive extremas of the normalized voltage exceeding a loss of isolation range threshold over a diagnostic window of time after detecting the normalized voltage exceeding the diagnostic activation threshold; and 
 automatically initiate a remedial action when the first number of instances of the range is greater than a loss of isolation detection threshold by automatically generating a diagnostic code associated with the electric motor. 
 
 
     
     
       18. The vehicle system of  claim 17 , further comprising an output device coupled to the control module, wherein the remedial action further comprises the monitoring service providing a user notification via the output device. 
     
     
       19. The vehicle system of  claim 18 , wherein the output device comprises a dashboard indicator and the user notification comprises illumination or activation of the dashboard indicator. 
     
     
       20. The vehicle system of  claim 17 , further comprising an energy source coupled to the DC voltage bus, wherein the DC voltage comprises an output voltage associated with the energy source.